Fuel injection systems are used on various engines to ensure not only reliable fuel delivery, but also to provide the flexibility of rate shaping to reduce emissions and noise levels. U.S. Pat. No. 5,492,098 issued to Hafner et al. on Feb. 20, 1996 shows a Hydraulically-Actuated Electronically-Controlled (HEUI) fuel system with a fuel injection rate shaping device that interrupts the flow of fuel injected during an injection cycle by spilling fuel from a high pressure fuel chamber in communication with an injector nozzle. The spilling is in response to aligning an opening in a slidable plunger with a port in a housing within which the plunger reciprocates.
While this design provides rate shaping, in some instances the injector's structural components are adversely affected by pressure waves induced by alternate high pressure fuel spillage and fuel flow obstruction. The initial spill of high pressure fuel from a chamber through an opening in the plunger into the port sends the fluid at a high velocity into the stationary port. As the plunger continues its motion, the opening moves out of alignment with the port and the spill is rapidly shut off. These operating dynamics may result in cavitation which causes structural wear of the components, primarily at the sharp intersection corners of the port and a bore and on the plunger itself as it moves past the port opening.
U.S. Pat. No. 5,292,072 issued to Rix et al. on Mar. 8, 1994, addresses the issue of high pressure fluids inducing wear at the intersection of two bores at a sharp edge, having a very small radius. Here, a method for machining such intersections to have a greater radius at the intersection point is discussed. However, such an approach in the rate shaping device of a fuel injector may undesirably reduce the rapidity with which fuel spill can be initiated and terminated to preserve sharp injection rate shaping that is essential to achieving lower emissions levels.
The present invention is directed to overcoming one or more of the problems as set forth above.